ARM64: dts: Add PSCI cpuidle support for MSM8916

Add device bindings for CPUs to suspend using PSCI as the enable-method.

Cc: <devicetree@vger.kernel.org>
Signed-off-by: Lina Iyer <lina.iyer@linaro.org>
Tested-by: Andy Gross <andy.gross@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>